Solenoid actuators can be used to control fluids (liquids and gases), or for positioning or for control functions. A typical example of a solenoid actuator is the fuel injector. Fuel injectors are used to inject pressurized fuel into a manifold, an intake port, or directly into a combustion chamber of internal combustion engines. Known fuel injectors include electromagnetically-activated solenoid devices that overcome mechanical springs to open a valve located at a tip of the injector to permit fuel flow therethrough. Injector driver circuits control flow of electric current to the electromagnetically-activated solenoid devices to open and close the injectors. Injector driver circuits may operate in a peak-and-hold control configuration or a saturated switch configuration.
Fuel injectors are calibrated, with a calibration including an injector activation signal including an injector open-time, or injection duration, and a corresponding metered or delivered injected fuel mass operating at a predetermined or known fuel pressure. Injector operation may be characterized in terms of injected fuel mass per fuel injection event in relation to injection duration. Injector characterization includes metered fuel flow over a range between high flow rate associated with high-speed, high-load engine operation and low flow rate associated with engine idle conditions.
It is known for engine control to benefit from injecting a plurality of small injected fuel masses in rapid succession. Generally, when a dwell time between consecutive injection events is less than a dwell time threshold, injected fuel masses of subsequent fuel injection events often result in a larger delivered magnitude than what is desired even through equal injection durations are utilized. Accordingly, such subsequent fuel injection events can become unstable resulting in unacceptable repeatability. This undesirable occurrence is attributed to the existence of residual magnetic flux within the fuel injector that is produced by the preceding fuel injection event that offers some assistance to the immediately subsequent fuel injection event. The residual magnetic flux is produced in response to persistent eddy currents and magnetic hysteresis within the fuel injector as a result of shifting injected fuel mass rates that require different initial magnetic flux values.